1. Field of the Invention
This invention relates to apparatus and method for processing polyurethane foams to form bicycle tires and the like.
2. Prior Art
For several years now polyurethane foams have been used to produce products having outer integral skins surrounding or partially surrounding a core. It has been recognized, for example, that bicycle tires and wheelchair tires can be produced having an outer integral skin and a solid core. Such products have gained acceptance, because they give a ride that is rather comparable to pneumatic tires while not being subject to loss of air through punctures, blow-outs, etc. The previously known products, however, have been of inconsistent quality, frequently having areas in the finished part which will vary in density. Such density variances, result in inconsistent wear of the tires and will not provide consistent comfortable riding qualities.
3. Objects of the Invention
Principal objects of the present invention are to provide an apparatus and method useable in the production of non-pneumatic tires, and other products that will have a tough outer integral skin surrounding a foamed inner core of uniform density.
Other objects are to provide a non-pneumatic tire that will provide the ride and comfort of a pneumatic tire, while having greater wear-life and not subject to puncture or blow-out.
In the past, solid polyurethane tires, semi-pneumatic polyurethane tires, solid rubber tires, and solid tires made of other materials, have been proposed. Polyurethane foams have also been used, but the variation of density throughout the finished product, together with voids and blemishes in the product surface have greatly limited the acceptance of the products produced.
It is therefore, another object of the present invention to provide apparatus and method for producing articles from polyurethane foams that have uniform density throughout the cores thereof and integral surfaces free of voids, blemishes and other defects.
Another object of the invention is to produce a non-pneumatic tire at a cost that will allow such tire to compare favorably in the marketplace with pneumatic tires.
Yet another object is to provide a non-pneumatic tire, that is not subject to loss of air as a result of punctures and blowouts, but that will still provide the ride characteristics of a pneumatic tire.
4. Features of the Invention
Principal features of the apparatus of the invention include a mold holder, including means to position an article forming mold thereon in surrounding relationship to a distribution plate and a clamping plate adapted to engage the mold whereby the mold is sandwiched between the mold holder and the clamping plate. The mold holder and clamping plate are mounted to spin about a common central axis, to thereby spin the mold secured between them. A drive motor is provided to drive a shaft of the mold holder to obtain the desired spinning action.
A resin supply head receives the components of the resinous material used to make the polyurethane foam and supplies the materials through a feed tube through the clamping plate and onto the distribution plate.
The mold is made to encircle the distribution plate and has an inner circumferential opening at the level of the top surface of the distribution plate, whereby, materials supplied to the distribution plate through the inlet tube will, upon spinning of the mold holder, clamping plate, and mold therebetween, be distributed evenly into the mold.
The method of the present invention involves using polyurethane foam mixes formulated such that cells of the foam projected against the surface of a host mold collapse as the bulk of the foam is forced into the mold and against the cells at the wall. The collapsing cells form a tough skin for the product being molded and the collapse of the cells is more rapidly developed and improved by the rotation of the mold about acentral axis. The rotation of the mold also results in a foamed core, surrounded by the tough outer skin, with the core being of uniform density, throughout the article produced. The speed of rotation of the mold is predetermined to achieve desired skin thickness and consistency. It is also possible to use varying speeds of rotation speeds correlated to the various stage of polymer growth to enhance the forming mass in the production of molded items with uniform skins, surrounding uniform inner cores of foam.
The foam mixture used comprises conventional polyisocyanates and polyols and water. Halogenated aliphatic hydrocarbon blowing agents may also be used along with the water. Also, silicone surfactants may be used to maintain a fine uniform stable bubble for cell development. Alternatively, freon may be added to the mix to provide for proper foaming and uniform density of the core of the product.
While the apparatus and process are here disclosed as being suitable for the production of bicycle tires, it will be apparent that other items can be produced by chaning the shape of the mold used.
Additional objects and features of the invention will become apparent from the following detailed description and drawings, disclosing what is presently contemplated as being the best mode of the invention.